This invention relates to a method of measuring the concentration of a substance or determining a reaction process caused in a sample solution, using scattered light. Particularly, the invention relates to a method which provides accurate understanding of partial reaction and effective removal of abnormal scattered light.
The measurement of scattered light is suited to the analysis of a reaction solution accompanied by the behavior of suspended material, because it is non-contacting with the reaction solution and more sensitive than tubidimetry. It is widely used in the field of clinical examination such as the measurement of various antigen-antibody reaction and blood coagulability test.
The conventional methods of scattered light measurement, however, have a drawback that they are susceptible to abnormal scattering due to dust or air bubbles mingled in the test solution, because they measure scattered light from a light beam incident upon the test cell in a relatively wide area. Particularly, when the concentration of the object to be measures is low and the level or change of the signal is small, the influence of abnormal scattering is remarkable, resulting in decreased reliability of measurement. To minimize the influence, a system is used in which light flux is applied to only a small part of the measuring cell. In this case, however, any dust or air bubble if present in the position where the light flux is applied can exert larger influence than that when light flux is applied to larger area.
To solve this problem another method (Japenese Laid-Open Patent Application No. Sho 57-23884) provides a noise detector independently from the detector for measuring the sample solution and remove the measurement signal obtained at the time when a noise is detected, from the calculation. In this technique, however, only one series of signals from a cell, or when dust, etc. are detected, a series of signals with a gap or gaps at the spot are obtained. When the gap or gaps are present in a significant position where the reaction process is determined, the measurement becomes meaningless.
Further, this Laid-Open Patent Specification No. Sho 57-23884 changes the relative position of the light flux application to the measuring cell whenever scattered light from dust, etc. is detected, or continuously moves the relative position during measurement to minimize the time the dust particle, etc. are in the flux. This method, however, is inaccurate since it treats the scattered light signals from different regions in the measuring cell without distinction to avoid the influence of dust, etc. When examining a reaction process, in particular, changing signals due to the difference of measuring region in the cell disturb the detection or reaction progress. This is fatal to the detection of reaction progress such as blood coagulability test and to reaction rate measurement.
In blood coagulability test, the coagulation time is defined as the time when fibrin separation begins to occur partially. When detecting the point where the reaction occurs partially, application of light flux over a wide range results in a small change rate of scattered light output and in poor reproducibility being susceptible to dust and air bubbles.